Catalytic combustion systems are being developed for heavy duty industrial gas turbines in order to achieve extremely low levels of air polluting emissions in the gas turbine exhaust. The emissions to be minimized include the oxides of nitrogen (NOx), carbon monoxide (CO), and unburned hydrocarbons (UHC).
From the outset, it has been recognized that a very uniform flow field would be required at the catalytic reactor inlet in order to meet the emissions performance objectives for the system and obtain the desired service life from the catalytic reactor. Indeed, to function properly, the catalytic reactor in a catalytic combustor must be supplied with an inlet flow field which is uniform in temperature, velocity, pressure and fuel/air concentration distribution. If the catalytic reactor is furnished with a non-uniform flow field at the inlet, two adverse consequences will result. One, the useful service life of the catalytic reactor will be reduced and, two, the emissions performance of the catalytic combustion system will be degraded. These problems result because non-uniform temperature distributions will occur within the catalytic reactor and in the post catalyst reaction zone where the chemical reactions of combustion are completed. Regions of higher than average temperature within the catalytic reactor, so-called xe2x80x9chot spotsxe2x80x9d, will shorten the reactor life by increasing thermal stress and accelerating certain reactor degradation mechanisms such as sintering and oxidation. Regions of higher than average temperature in the post catalyst reaction zone may produce thermal NOx if the local temperature exceeds the thermal NOx generation threshold. This could prevent the system from achieving extremely low NOx levels. Regions of lower than average temperature in the post catalyst reaction zone can cause local quenching of chemical reactions, which results in an increase in CO and UHC emissions. Therefore, uniformity of temperature distribution within the catalytic reactor and in the downstream reacting flow field is important to meeting reactor life objectives and emissions performance objectives.
U.S. Pat. No. 4,966,001, the entire disclosure of which is incorporated herein by this reference, has issued covering a multiple venturi tube (MVT) gas fuel injector for catalytic combustor applications. One objective of this device was to achieve a very uniform fuel/air mixture strength distribution at the catalytic reactor inlet by uniformly distributing the gas fuel over the entire hot gas flow section approaching the catalytic reactor inlet. This device has been used for several laboratory test programs to develop catalytic combustion for heavy duty industrial gas turbines, but the objective for fuel/air mixture strength distribution uniformity at the catalytic reactor inlet (less than +or xe2x88x925% deviation from the mean) has not been achieved.
The primary reason for non-uniformity of fuel/air concentration distribution exiting the MVT main fuel injector is non-uniform velocity distribution (mass flux per unit area) in the hot gas flow entering the MVT main fuel injector.
The invention is embodied in a device for conditioning the flow of hot gas in a catalytic combustor in preparation for entry into a catalytic reactor. As explained above, to function properly, the catalytic reactor must be supplied with hot gas flow which is uniform in temperature, velocity, pressure and fuel/air concentration distribution. Accordingly, the invention is embodied in a device for obtaining the uniform flow field required by the catalytic reactor when it is supplied with a non-uniform flow field by upstream components of the catalytic combustor.
The flow conditioner of the invention causes the velocity distribution of the hot gas flow entering the MVT main fuel injector to be more uniform which will result in a more uniform fuel/air concentration distribution and velocity distribution at the catalytic reactor inlet. This will increase the service life of the catalytic reactor by avoiding xe2x80x9chot spotsxe2x80x9d and will improve the emissions performance of the catalytic combustion system.